1. Field of the Invention
The present invention relates to electronics cards and, more particularly, to an electronics card with an alignment opening.
2. Description of the Related Art
A card cage is a structure, typically metal, that includes pairs of edge supports that support a number of electronics cards. FIG. 1 shows a front-side perspective view that illustrates a prior-art card cage 100. As shown in FIG. 1, card cage 100 includes a metal structure 110 that has a series of edge support pairs ES1-ESn.
The members of each edge support pair ES1-ESn are substantially vertically in register with each other to support a corresponding number of electronics cards, such as electronics card EC. Insertion of electronics card EC into card cage 100 requires that card EC be placed between a pair of edge supports ES, such as edge support pair ESn, and then slid into cage 100 in the direction shown by arrow 112. (Although FIG. 1 shows the electronics card EC vertically held by card cage 100, electronics cards can also be held horizontally by a card cage.)
When multiple electronics cards are held by card cage 100, the electronics cards communicate with each other via another electronics card which is commonly known as a backplane. The backplane, which is connected to the back side of card cage 100, has a number of connectors that engage the connectors on the electronics cards when the electronics cards have been fully inserted into card cage 100.
FIG. 2 shows a back-side perspective view that further illustrates prior-art card cage 100. As shown in FIG. 2, card cage 100 holds a series of electronics cards EC1-ECn that has a corresponding series of first connectors CT1-CTn. The first connectors CT1-CTn, which are shown as blocks in the figure, can be implemented with any electronics card connector.
In addition, an electronics card 210, such as a backplane, which is shown in a cut away view, is connected to the back side of card cage 100. Electronics card 210 has an inner surface 212, an outer surface 214, and a series of second connectors CN1-CNn (connector CN1 is not shown in the cut away view) formed on inner surface 212 that engage and form an electrical connection with the first connectors CT1-CTn when the electronics cards EC1-ECn have been fully inserted into card cage 100.
Although not shown in FIG. 2, electronics card 210 includes a number of internal electrical routing paths that are connected to each of the second connectors CN1-CNn. The internal electrical routing paths, in turn, form the physical portion of a number of card-to-card data busses and control lines.
To insure that a first connector CT and a second connector CN engage when an electronics card EC is slid into card cage 100, electronics card 210 must be precisely aligned to card cage 100 when electronics card 210 is attached to card cage 100. Without the precise alignment of electronics card 210, the first connectors CT and the second connectors CN are unable to mate when electronics card EC is inserted into card cage 100.
To aid in the alignment of electronics card 210 when electronics card 210 is attached to card cage 100, card cage 100 includes a number of alignment tabs that extend away from metal structure 110, while electronics card 210 includes a corresponding number of alignment openings that are formed through electronics card 210. When electronics card 210 is attached to card cage 100, the alignment tabs fit snugly in the alignment openings.
The alignment openings through electronics card 210 can be formed by first drilling a hole through electronics card 210 using a drill bit with a first diameter, such as 2.362 mm (0.093 inches). Following this, the hole is routed along a straight line using a routing bit that also has the first diameter to form an alignment opening with rounded ends.
FIG. 3 shows a partial end view of card cage 100 that additionally illustrates electronics card 210. As shown in FIG. 3, card cage 100 includes an alignment tab 310 that extends away from the back side of cage 100. Alignment tab 310, in turn, has a length L1 and a thickness T.
In addition, electronics card 210 has an alignment opening 312 formed through electronics card 210 that is precisely dimensioned in length to accept alignment tab 310 when electronics card 210 is attached to card cage 100. Alignment opening 312 is formed as described above using a drill and a router to have a maximum length L2 and a width W. Due to the curved ends of alignment opening 312, length L1 is less than maximum length L2.
However, as shown in FIG. 3, when the thickness of the metal used to form the alignment tabs is less than the diameters of the drill and router bits used to form alignment opening 312, only the four corners of alignment tab 310 can be brought into contact with the side walls of alignment opening 312 when alignment tab 310 is inserted into alignment opening 312.
When only four corners can be brought into contact with the supporting side walls, any rotational pressure placed on electronics card 210 from handling and assembly is concentrated at the four corners. Similarly, any longitudinal pressure (along the length of tab 310) placed on electronics card 210 from handling and assembly is concentrated at two of the corners.
When sufficient rotational or longitudinal pressure is exerted on electronics card 210, alignment opening 310 becomes deformed which, in turn, causes tab 310 to fit loosely within opening 312. When tab 310 fits loosely within alignment opening 312, a precise alignment can not be made.
As a result, a fixture or other device is commonly used to insure that electronics card 210 is precisely aligned to card cage 100 when electronics card 210 is attached to card cage 100. Although electronics cards can be attached to card cages using this fabrication approach, the fixtures can be costly to build, maintain, and utilize.
One approach to reducing deformation due to rotational pressure is to form the alignment openings with widths (which are defined by the diameter of the drill and router bits used to form the openings) that are substantially the same size as the thicknesses of the alignment tabs. As a result, the sides of the alignment tab contact the sides of the alignment opening.
Although this approach reduces deformation due to rotational pressure, potential deformation due to longitudinal pressure remains a problem. Another drawback to this approach is that the smaller drill and router bit sizes that must be used are non-standard which, in turn, significantly increases the fabrication costs of the electronics card. Drill and router bit sizes that are substantially less than, for example, 2.362 mm (0.093 inches), are not commonly used due to reliability and lifecycle concerns.
Thus, there is a need for a method of precisely aligning an electronics card, such as a backplane, to a structure, such as a card cage, when the electronics card is attached to the structure that eliminates the need for a fixture without using non-standard drill and router bit sizes.